SHAO Astrophysics Colloquium

Title: Ultra-compact dwarf galaxies (UCDs) in the Virgo cluster

Speaker: Chengze Liu (Shanghai Jiao Tong University)

Time: 3:00 pm, January 09 (Thursday)

Location: Lecture Hall, 3rd floor

Abstract: 

For many decades, it was widely believed that galaxies and star clusters were completely distinct populations. However, in the late 1990s, a new type of compact stellar system, Ultra-Compact Dwarf (UCD) galaxies, was discovered to have some properties that bridged the gap between compact, dwarf galaxies and globular clusters. Roughly 20 years after their discovery, the origin of UCDs remains surprisingly obscure. In this talk, I will present results for UCDs in the Virgo cluster based on imaging mainly from the Next Generation Virgo Cluster Survey (NGVS). We have identified more than 600 candidate UCDs from the cluster core to the virial radius. This is the largest and most homogeneous sample of UCDs presented to date for any cluster environment, and the first of its kind for the Virgo cluster. I will summarize the basic statistical properties of the UCD sample, compare to the GCs and nuclei, identify any special UCDs we found and give the observational constrains on the origin of UCDs.

Seminar talk

Title: GR effects in black hole accretion flows

Speaker: Andrzej Nied？wiecki

Time: 10:00 am, January 07 (Tuesday)

Location: xxx, 3rd floor

Abstract: I will discuss strong gravity effects relevant for the formation of X-ray spectra in the optically-thick as well as the optically-thin regime of black hole accretion, and results of investigation of these effects in several black hole systems: 1H0707-495, NGC 4151 and NGC 7213.

About the speaker: Andrzej Nied？wiecki is currently an associate professor at the Department of Astrophysics at the University of ？ód？ (？ód？, Poland). From 1992 to 1997 he worked at the Copernicus Astronomical Center of the Polish Academy of Sciences in Warsaw, where he received the Doctoral Degree in 1996. In 1997 he moved to the University of ？ód？, where he got the habilitation in 2009. His scientific interests fall in two areas of high energy astronomy and astrophysics: (1) theoretical and observational investigation of accretion onto compact objects, and (2) experimental techniques of imaging Cherenkov telescopes (ICT). He is involved in two ICT experiments, MAGIC and CTA.